Microelectrode studies are being conducted in the vestibular nerve and vestibular nuclei of the squirrel monkey (Saimiri sciureus). The goal of the project is the elucidation of the function of the various peripheral endorgans in primates and of the ways in which information encoded peripherally is transformed in central pathways. Specific research goals for the coming year are: (1) Use of both electrical and mechanical stimulation in an attempt to dissect the various states of the sensory transduction process. (2) Studies of the functional organization of the vestibular nuclei will continue, with particular emphasis placed on the descending and lateral vestibular nuclei and on the y group. We are particularly interested in ascertaining whether there are central neurons exclusively related to the otolith organs, since such neurons were only rarely encountered in our previous studies of the superior and medial vestibular nuclei. (3) The responses of vestibular afferents to rotations about an earth-horizontal axis will be investigated, since such stimuli lead to peculiar (and as yet unexplained) reactions of the entire vestibular system. (4) Methods will be developed so that we can record from unanesthetized, behaving animals. Our main interest here is in exploring possible functions of the efferent vestibular system by recording both from the efferents themselves and from peripheral afferents.